Extensional Flow of Polymer Melts

Abstract

The apparent uniaxial extensional viscosity or elongational viscosity, ηE, of several polymer melts in a wide range of temperatures was determined as a function of strain rate, ε̇, using Cogswell's analysis of converging flow at the die entry. In particular, ηE was derived from knowledge of the dependence of the steady-flow viscosity as well as the entrance pressure drop, δP0, on shear rate. Quantitative agreement was found in ηE−ε̇ dependence derived from the convergent flow analysis (CFA) along with that measured from isothermal melt-spinning experiments for melts of high-density and low-density polyethylene, polypropylene, and polystyrene. Further support of CFA comes from the finding here that the normalized entrance pressure drop, δP0/τ, is uniquely related to the vortex angle in a manner similar to that determined from flow visualization studies by Ballenger and White. Here τ is the shear stress at the die wall. Additionally, the flow activation energy in extension is found to be equal to that in shear for melts of low-density polyethylene, polypropylene, and polystyrene. Such observations are in line with the earlier results of Munsted on polystyrene melts. An anomaly exists for high-density polyethylenes since ηE increased with increases in temperature above a critical temperature. Finally, the shapes of extensional flow curves are found to be similar to the published data, although an exception such as low-melt-index, low-density polyethylene, where ηE decreases with ε̇, is cited.

Thickness difference of electrode coatings caused by elastic turbulence of electrode compounds under condition of nonisothermal pressure flow

“…In such a form Bagley correction was used as a basis for evaluation of value of natural convergence angle, which is formed in pre-capillary zone at extrusion processing of visco-elastic materials [11][12][13].…”

Characterization of biofiber breakage in composite processing using a capillary rheometer

“…19,20 Cogswell theory is widely used to calculate extensional viscosities from capillary rheometers. 21–24

Figure 1.A schematic of the capillary rheometer with long and “zero-length” dies.

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“…19,20 Cogswell theory is widely used to calculate extensional viscosities from capillary rheometers. [21][22][23][24] In order to decouple the pressure drop that occurs in the capillary die from that of the excess pressure drop, both bores have dies of equal diameter but of different lengths. One bore used a 16-mm length die.…”

Validation of Cogswell's convergent flow analysis

“…The "steady-state" elongational viscosity data were obtained from the capillary rheometer data described above and eq. (5).…”